Java语言的基础语法（二）

运算符

■赋值运算符：+=(加赋值)、-=（减赋值）、*=（乘赋值）、/=（除赋值）、%=（求余赋值）

   例：   

int i=5;
int j=10;
i +=j;    等价于i=i+j;

■算数运算符：+、-、*、/、%、++（自增运算符）、--（自减运算符）

   ※※注意：●++（--）

                       ●在前时先运算后取值

                       ●在后时先取值后运算

■比较运算符：>、<、>=、<=、==、!=

■逻辑运算符：！（逻辑非）、&（非简洁逻辑与）、&&（简洁逻辑与）^（逻辑异或）……

■位运算符：~（按位取反）、&（按位与）、^（按位异或）<<（左移）>>（右移）>>>（无符号右移）

例：59<<1=119等价于59*2^1=119

条件选择语句
1、基本if条件语句                2、if…else语句                         3、if多分枝语句                         4、switch……case多分支语句

  if(判断条件){                           if（判断条件）{                            if（判断条件1）{                         switch(表达式){

       执行语句（代码块）                执行语句（代码块）;                执 行语句（代码块）;           case   常量值1：

}                                                  }else{                                             }else if(判断条件2 ){                          执行语句1（代码块）;                        

                                                           执行语句（代码块）;                执行语句（代码块）;                   break;                  

                                                     }                                                    }                                                      case  常量值2：

                                                                                                                  ……                                            执行语句2（代码块）;                        

                                                                                                            else if（判断条件n）{                       break;

                                                                                                                   执行语句（代码块）;                ……

                                                                                                           }                                                      case   常量值n:

                                                                                                                                                                         执行语句n（代码块）; 

                                                                                                                                                                          break;
                                                                                                                                                                     default;
                                                                                                                                                                           执行语句n+1（代码块）;    
                                                                                                                                                                           break;
                                                                                                                                                                      }
 
循环控制语句  
1、while循环语句             2、do……while循环语句           3、for循环语句
while（表达式）{                do{                                                   for（初始化部分；条件判断部分；迭代因子）{
          循环体                                循环体                                                  循环体
}                                             }while(循环条件);                            }
 
4、for循环的嵌套
例：使用for循环多重嵌套打印九九乘法表

public class TestForNested{
public static void main(String[] args){
for(int i=1;i<=9;i++){
for(int j=1,j<=i;j++){
System.out.print(i+"*"+j+"="+i*j+"\t");
}
System.out.println();
}
}
}

流程控制语句

 
1、继续语句continue
不带标号的（continue；）：程序的执行流程跳出本次循环。

带标号的（continue  标号名；）：转向去执行标号名所标识的循环层次。
2、返回语句return
语法格式：     return  [表达式];
其中，表达式是可选参数，表示返回时所需要带回的值。
3、退出语句break
不带标号的（break;）：用于循环语句和条件选择语句的终止运行，直接执行其后面的语句。
带标号的（break  标号名）：作用是让程序运行到带标号的break语句时，从标号名所标识的整个程序块中跳出。